Tower-mounted receivers are well known in the context of solar energy collector systems and may take various forms, depending upon whether they are employed, for example, in the transfer of radiative energy to photovoltaic cells or in the transfer of thermal energy to a heat exchange fluid such as water, a molten salt or air.
More efficient tower-mounted receivers may incorporate a cavity having a relatively small aperture through which concentrated (reflected) radiation is focused from a field of reflectors and, in receivers that have relevance to the present application, provision is made for the transporting of thermal energy that is generated within the receiver as a consequence of absorption of solar energy in the wall of the cavity. However, these receivers do not make specific provision for integrated storage of thermal energy that is generated in the receiver by absorption of solar energy.
A solar energy receiver that does provide for integrated thermal energy storage is disclosed in U.S. Pat. No. 4,815,443, issued Mar. 28, 1989, and assigned to Rockwell International Corporation ('443 patent). However, the receiver as described in the '443 patent has specific application to a space station. There, the receiver comprises a first (helical-form) fluid conduit that is located within a cavity of the receiver, and a second fluid conduit that is located within a thermal energy storage layer that is formed from a metallic material that surrounds the cavity. The first conduit and the thermal energy storage layer are both exposed to solar radiation that is focused into the cavity during insolation periods. During these in-sun periods, a first heat exchange fluid is cycled through the first conduit. A second heat exchange fluid is cycled through the second conduit during in-shadow periods. The first and second heat exchange fluids are then used alternately for heat exchange with a working fluid that is used to energize an associated heat engine.
Also of relevance to the present application is a thermal energy storage system as disclosed in International Patent publication WO2005/088218, by Larkden Pty Ltd, in which a substantially solid body of graphite is employed to store heat energy for subsequent release to a fluid through surface-mounted heat exchangers. However, in this system, as disclosed, thermal energy is generated in the graphite body by electrical resistance heating in a cavity within the graphite body.
A need exists for improved receivers to be used with tower solar arrays (e.g., a multi-tower solar array), and in particular, receivers that include integrated thermal energy storage.